Teen dating violence (TDV) among urban youth has numerous immediate and long-term consequences. Most notably, exposed youth are more likely to be depressed, do poorly in school, binge drink, smoke, use/abuse substances, attempt suicide, have risky sex, be in physical fights and be re-victimized both as teens and adults. Over 40% of respondents in the nationally representative Add Health longitudinal study reported TDV victimization by young adulthood; for 12 years, 9% of high school students report past year victimization in the Youth Risk Behavior Surveillance System. To date, no TDV preventive interventions exist in the scientific literature that are delivered in urban, high-risk neighborhoos to middle school aged youth, despite higher risk of TDV among youth of color and lower SES and the developmental appropriateness of raising awareness of and teaching skills to prevent TDV to youth who are just starting to form romantic relationships. Start Strong Boston is an innovative, theory-driven TDV and healthy relationship intervention for youth ages 11-14 years attending afterschool programs in Boston's highest crime neighborhoods. Developed by the Boston Public Health Commission (BPHC) as part of a national program, it has shown feasibility and acceptability when delivered in 3-5 afterschool programs annually since 2009, delivered by Peer Leaders ages 15-18. It receives local, national and global press especially for innovative media literacy components. Start Strong Boston is ready for the next steps in its development into an evidence-based program: refining and determining which elements to include in a testable, manualized program, and evaluating feasibility and acceptability to conduct a rigorous cluster- randomized efficacy trial in Boston, MA using youth participatory action research (YPAR) methodology in a future R01. This study will provide additional development work needed to refine elements that should be replicated with fidelity (curriculum, outreach strategies and peer-leadership components); refine and pilot-test survey measures, participant tracking procedures, trainings for Peer Researchers; and determine acceptability by programs to be randomized. This proposal is a collaboration between the Institute on Urban Health Research and Practice at Northeastern University and the BPHC to (1) develop and refine the Start Strong Boston intervention and evaluate its cultural competence among diverse urban youth; (2) assess feasibility and acceptability of a future longitudinal, cluster-randomized trial of Start Strong's efficacy; and (3) assess feasibility of participatory methods to involve teens as Peer Leader facilitators and as Peer Researchers. Following the Stage Model of Behavioral Therapies Research, we will use formative and process evaluation data collection and analysis of both qualitative and quantitative data to move Start Strong Boston from Stage I to Stage II in intervention development. We will deliver a manualized intervention ready for an efficacy trial, in order to eventually provide the field with the first efficacious, multilevel TDV preventive intervention for middle school age children and their high school-aged peer mentors in urban afterschool programs in high-risk neighborhoods.